"No Render output node in scene" rendering a simple animation
This means you're using Compositing nodes but haven't fed anything to the output node or don't even have one.
Either you don't need compositing, in which case you just open the compositing editor and uncheck the use nodes option in its header, or you connect some output node.

The usual one is the Composite:



A simple one, you just plug whavetver you want to have at the end in its Color input. That's basically a node saying to blender "I want this as a final result". There are plenty of other outputs nodes you can try too. But that's the one you will use more often than not.